Halo of a high-brightness electron beam

The experimental study of transverse profile of the ELSA-linac electron beam has been undertaken in order to analyze the mechanisms of halo formation and development in the generation, acceleration and transport of a high-intensity, high-brightness charged-particle beam. Measurements are reported in which the beam profile is observed over four to five decades. They were performed using an imaging technique in which light emitted from an optical transition radiation (OTR) screen placed in the beam path is transported through conventional optics to an intensified video camera. The electron-density distribution is shown to be dependent on the beam current, through space charge effects, initial conditions and transport configuration.